Apparatus for sharpening blades

ABSTRACT

An endless abrasive belt runs on a contact wheel and on an idler wheel to perform grinding and sharpening operations on a rotary lawnmower blade. The cutting edges of such a blade are on the outermost ends thereof, and are each defined by the intersection of the flat face side of the blade and a surface ground away at an acute angle with the flat face of the blade. For each cutting edge, there is a taper back to the outer leading edge of the bar stock of which the blade is made. The grinding or sharpening is done in the usual manner for abrasive belt grinding wherein an endless coated abrasive belt is backed by a contact wheel having a cylindrical backup face, but the edge of the contact wheel adjacent the taper is relieved on a radius, and the endless belt extends out over this relieved radius and past the outer edge of the contact wheel. When the work is pushed against the abrasive belt and contact wheel, the grinding pressure exerted by the belt extending out over the radius and past the wheel varies from full pressure at the point where the relief starts, out to the outer edge of the belt where the only pressure is that occasioned by the centrifugal action of the abrasive belt itself. The result achieved is a smooth, even taper from the point of full contact with the wheel to a point where the abrasive belt is no longer in contact with the workpiece.

lluited States Patent 1 Wintz i111 3,896,592 July 29,1975

[73] Assignee: Aladdin Manufacturing Company, 1

Minneapolis, Minn.

22 Filed: May 6, 1974 21 Appl. No.: 467,009

[75] Inventor:

152] U.S.Cl. ..51/135 R;5l/l4l [51] Int. Cl. B24B 21/12; B24B 3/40 [58] Field of Search 51/135 R, 141, 285, 288; 76/82.]

[56] References Cited UNITED STATES PATENTS 1,704,827 3/1929 Furber 51/135 R 2,257,864 10/1941 Shechan 51/141 2,637,956 5/1953 Nucsslc 5l/407 2,751,723 6/1956 Lindmark 51/135 R 3,369,328 2/1968 Frcerks 51/135 R 3,516,207 6/1970 Badcr 51/135 R Primary Examiner-Al Lawrence Smith Assistant Examiner-Nicholas P. Goclici [57] ABSTRACT An endless abrasive belt runs on a contact wheel and on an idler wheel to perform grinding and sharpening operations on a rotary lawnmower blade. The cutting edges of such a blade are on the outermost ends thereof, and are each defined by the intersection of the flat face side of the blade and a surface ground away at an acute angle with the flat face of the blade. For each cutting edge, there is a taper back to the outer leading edge of the bar stock of which the blade is made, The grinding or sharpening is done in the usual manner for abrasive belt grinding wherein an endless coated abrasive belt is backed by a contact wheel having a cylindrical backup face, but the edge of the contact wheel adjacent the taper is relieved on a radius, and the endless belt extends out over this relieved radius and past the outer edge of the contact wheel. When the work'is pushed against the abrasive belt and contact wheel, the grinding pressure exerted by the belt extending out over the radius and past the wheel varies from full'pressure at the point where the relief starts, out to the outer edge of the belt where the only pressure is that occasioned by the centrifugal action of the abrasive belt itself. The result achieved is a smooth, even taper from the point of full contact with the wheel. to a point where the abrasive belt is no longer in contact with the workpiece.

2 Claims, 5 Drawing Figures PATENTEDJUL29I9Y5 3,896,592

SHEET FIEE 1 APPARATUS FOR SHARPENING BLADES BACKGROUND OF THE INVENTION jacent the pointwhere the ground surface terminates.

Even where the workpiece is provided with an initial taper between the end of the edge to be groundand the edge of the workpiece not to be ground, the abrasive belt will eventually, if not initially, snag and/or wear out along this outer edge portion long before the normal belt wear is achieved on the other portions of the belt.

Heretofore the suggested solution to this problem was to cut away or stamp out a circular area between the end of the elongated edge to be ground and that portion of the workpiece not to be ground or sharpened. This solution is not economically viable because it introduces a completely nonproductive extra step into the processof making products such as ordi-' nary lawnmower blades where such edges are needed. This increases the price of production of such workpieces to the point where they are not economically saleable.

BRIEF SUMMARY OF THE INVENTION An endless abrasive belt is assembled on a Contact wheel and an idler wheel in the usual manner, but the edge of the contact wheel is relieved on a radius beginning at a point where the full grinding effect on the work is to terminate and where'a taper from a ground surface to an "unground surface is to begin. A belt is used which is wide enough to extend beyond the outermost relieved edge of the contact wheel.

A workpiece having a longitudinal edge on which a cutting edge is to be ground is held in any usual or preferred manner and is forced against the moving abrasive belt and against the contact wheel behind it. The desired surface will be ground in the usual manner, and

also, a taper will be produced beginning from the point of full contact of the abrasive belt and contact wheel with the work to the point where the work is no longer in contact with the belt.

IN THE DRAWINGS FIG. 1 is a side elevational view of a typical abrasive belt grinder set up to perform a grinding operation on a portion only of a longitudinally extending workpiece such as a rotary lawnmower blade, and showing the cutting face and cutting edge in accordance with the invention;

g 2 FIG. 4 is an enlarged fragmentary sectional view taken on the line 4--4 in FIG. 1; and

FIG. 5 is a sectional view on line 5--5 in FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENT:

A rotary lawnmower blade workpiece 10 is designed to be supported through central holes 12 therein on a rotary lawnmower and'to be rotated in direction to cause cutting edges 14 and 16 to cut grass as this mower is moved overthe grass. Upswept ends 18 and 20 on either end of, the blade serve as centrifugal fan blades, drawing air andsevered grass upwardly to be thrown from the mowing machine. Basically this blade 10 is made from flat, elongated bar stock and has a bottom blade face 26 and a parallel top blade face 28.

This invention deals with the efficient production of such blades, and specifically with the grinding away of parts of the edge of the bottom face 26 to form cutting faces 22 and 24 which intersect with top blade face 28 to form cutting edges 14 and 16, respectively.

The cutting faces 22 and 24 are produced by alternately clamping a first end 30 and then a second end 32 of the blade 10 in a hydraulically operated clamping fixture 34. This fixture includes a fixture block or pusher plate 66 which is sliddably mounted in a table block 36 on top of a table 38 and is propelled toward a contact wheel 40 by a table mounted linear hydraulic cylinder-piston motor 44 to force the blade 10 into the working surface of an endless abrasive belt 42.

The contact wheel 40 and endless abrasive belt 42 form a part of an abrasive belt grinder 46 which also includes'a stand 48, electric motor 50, and means 52 to drive the contact wheel 40 from the motor 50 is counterclockwise direction as seen in FIG. 1. Abrasive belt 42 is trained over idler pulley 54 which is rotatably mounted on stand 48.

Tie rods 56, 56 (one is shown) tie the table 38 to the stand 48 to withstand the pressure of the work against the contact wheel under the force of cylinder-piston motor 44.

OPERATION position as seen in dotted lines in FIG. 1 at the time the I workpiece 10 is first clamped in it.

Once this clamping action has taken place, the linear cylinder-piston motor 44 is activated to push the fixture block 66, and consequently the entire fixture 34 forward toiposition as seen in full lines in FIG. 1. At that time, the lawnmower blade workpiece l0 and the contact wheel 40 as well as the endless abrasive belt 42 will be positioned with respect to each other as seen in FIGS. 3, 4 and 5.

As seen inphantom inFIG. 3, the portion or first strip of the abrasive belt 42 which is backed up by the contact wheel 40 will, under the force of the ram or linear motor 44, grind away a relatively straight, flat surface or cutting face 22 thus to form a straight sharpened cutting edge 14 along a portion only of the bottom longitudinal edge of the lawnmower blade it). As best of the endless abrasive belt 4 2-extendsbeyond that V scribed by thatw'heelQ Thusg'bey ond the pointoftan seen in FIGIA, at leastone edge of the contact wheelff is relieved on aradius as indicated at 68. A second strip edgeofja contactwheelto the point where the u'nsiip-j portedbelt edge passes by the workpieceswithout com ing in contact'with it as the grinding progresses, r

' edge of the contact wheehand is, of course, not sup-'1" ported beyond the radius, except by its own Stiffness and by thecentrifugal force of its rapid movement with gency of therelieved portion of thegcontact wheel and :7

the cylindrical face of the wheel, the abrasive belt will 7 have something lesstha'n its full force and effect on the" 7 work being ground. Farther along the" abrasive belt to} ward the'unsupported edge'thereof, this force and set 7 feet becomes less and less, until the point is reached s "where there is no longer suffici'entsupport to force the f belt in against the'workpieceg'lhisresults in a tapered,

V grind smoothly outwardly from the'firs't strip backed ,by the cylindrical face ofthe cutting wheel to the outer edge of the cut.

Extensive tests have now shown that'there is: no e'xcessive wear on thelunsupported part of the belt; nor

is there any tendency for the'abrasive belt to catch on the workpiece when its unsupported endextends clear out past the point of contact between the belt and the workpiece. Belts used in accordance with'the present entire area of contact withthe cylindrical surface of the contact 7 wheel; and do not have to be replaced any extend beyond the edges of thecontact wheel;,

Contrary to this, andbefore-the present invention,

,d.'said cylindrical portion ofjsaid contact wheelproi V yiding a continuous cylindrical, support tothe first a "strip of said endless" abrasive belt; said 'first'astrip "thereby being adapted to grind astraight surface of? 'fastertha n belts used to grind materials which do not this kind'of sharpening was attempted with a structure;

gdrical portion of the contact wheel," 7

While the invention has been describedin connec tion with rotary lawnmower blades such'asi illustrated V ,7 i at 10 hereim itis'to' be understood thatthe'invention; V

jis'val'uable wherever an abrasive belt grinder'isto per 740; a a a a 5 I i i frpmthe straight surface ofrrtsfirstsecuon to i p r em ds eishti u f s w said--sewndY Y form a grinding operation along a certain portionofa;

piece which is to remain in the, 'ungr'ound' state.

' workpiece immediatelyadjacenttora portion ofa work-" 1 V The'essence' of the inventionincludes theluse ofan 25 V invention havebeen found to wear outevenly over the T cal surface." I

' While the'specification speaks of the contactwheel; 7' being relieved on a radius, it is tofbe understood that I this relief'could be atan angle, or could be tapered' or Y roundedjwithout involvement of a" circle segment; it i will be effectiveto go'frorn' full contact bythe'cyli'ndri-J r 1 cal portionjof a contact wheel to a point wherethe only outward ahrasive foree of the abrasive beltisiocca r ,r I V 'sioned by the stiffnessjofthe belt and'the' centrifugalac-K i k 7 tion of it as it andfthe contactwheel' 'moverapidly with s respect tofthe ivorkpiece; i I 1 V The embodiments oftheinventioninwhich an exclu siveproperty oruprivilege isclaimediaredefinedfas fol LAppara'tus for grinding alftirst sectionuonly of a f a work pieceha'ving' at'least first and second contiguous and continuous sections, said "apparatus including:

f a ,arotationally pbweredfeylindricalcontactiwheek fr I I1 bgan idle P l c. an endless abrasive belt havingia firststrip, opera l tively mounted for grinding 'onbth'e idlerpulley and r on a cylindrical portion ofsaid wheel and havingan integralsecond strip; extending beyond an edgelof l the contact'wheel;

i a first section of a work pieceeand wheel and being operative to abrade the work section.

the belt extends to'provide" a'lrelieyed portion soti proi gressively' lesserdiameteroutwardly fromsaidtcylindriit means tohold said first'sectionofsaidwork piece f I I f -iagainst said abrasiyebelt to force said cylindrical i support, surfacelof said wheel againstsaid .first'strip,

J T flsaid second strip of said belt,when said first season; of said workpiece issoiheld n aintaining a position r I i I inJspaced relation andfout ofrcontaet with said J e I 2.The[apparatusoi' clairn; saidjcontaet s 7 hen isrelievedalongtheiedgethereof beyond which 

1. Apparatus for grinding a first section only of a wOrk piece having at least first and second contiguous and continuous sections, said apparatus including: a. a rotationally powered cylindrical contact wheel; b. an idler pulley; c. an endless abrasive belt having a first strip operatively mounted for grinding on the idler pulley and on a cylindrical portion of said wheel and having an integral second strip extending beyond an edge of the contact wheel; d. said cylindrical portion of said contact wheel providing a continuous cylindrical support to the first strip of said endless abrasive belt, said first strip thereby being adapted to grind a straight surface of a first section of a work piece; and e. means to hold said first section of said work piece against said abrasive belt to force said cylindrical support surface of said wheel against said first strip of said belt; f. said second strip of said belt, when said first section of said work piece is so held, maintaining a position in spaced relation and out of contact with said wheel and being operative to abrade the work piece from the straight surface of its first section to a second section thereby to form in the work piece a taper from said straight surface to said second section.
 2. The apparatus of claim 1 wherein said contact wheel is relieved along the edge thereof beyond which the belt extends to provide a relieved portion of progressively lesser diameter outwardly from said cylindrical surface. 